Support grouped Progressive Syncs in ApplicationSets

[fm1ck3y]

Summary

Add support for grouping Applications in Progressive Syncs for ApplicationSets.

Currently Progressive Syncs work globally across all generated Applications. This makes it difficult to model independent rollout flows inside a single ApplicationSet.

Motivation

In real-world deployments, Applications are often logically separated into groups such as:

• clusters
• environments
• teams

Right now Progressive Syncs treat all Applications as a single rollout pipeline.

Example:

wave-1:

• app-a-dev
• app-a-prod

wave-2:

• app-b-dev
• app-b-prod

If app-a-prod is unhealthy, app-b-dev is also blocked, even though they are unrelated deployments.

This becomes especially problematic for multi-cluster or multi-tenant ApplicationSets where independent rollouts are expected.

Proposal

Add optional grouping support to RollingSync strategy.

Example:

spec:
  strategy:
    type: RollingSync
    rollingSync:
      groupKey: "environment"
      steps:
        - matchExpressions:
            - key: tier
              operator: In
              values: ["backend"]
        - matchExpressions:
            - key: tier
              operator: In
              values: ["frontend"]

Applications sharing the same groupKey label value would progress independently through waves.

Example:

dev:
  backend -> frontend

prod:
  backend -> frontend

instead of:

all backends -> all frontends

This would allow safer and more scalable progressive deployments while keeping existing behavior unchanged when groupKey is not specified.

[pjiang-dev]

Hi @fm1ck3y

I feel like the right fix here is probably just to use two separate ApplicationSets:

  # applicationset-dev.yaml  → backend-dev wave 0,
  frontend-dev wave 1
  # applicationset-prod.yaml → backend-prod wave 0,
   frontend-prod wave 1

This will have clean separation, independent rollout pipelines without needing to split expressions in a single AppSet.